UsingVhost

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As of September 2010, vhost is not included in any released tarballs, so you need the git version.

Vhost provides better latency (10% less than e1000 on my system) and greater throughput (8x the normal virtio, around 7~8 Gigabytes/sec here) for network.

Obtaining the code

git clone git://git.kernel.org/pub/scm/virt/kvm/qemu-kvm.git
git checkout refs/remotes/origin/stable-0.13
cd kvm
compile as usual

kernel requirements

On the host you need a kernel with CONFIG_VHOST_NET=y and in the guest you need a kernel with CONFIG_PCI_MSI=y

example command line

To start a guest with vhost:

/usr/bin/kvm -netdev type=tap,id=guest0,script=kvm-ifup,vhost=on -device virtio-net-pci,netdev=guest0,mac=00:16:3e:00:00:01 ..other options..